Hi @junayedhassan,
Sure, I will be happy to assist you in resolving your product permalinks issue. ??
Cloudflare Cache
Upon reviewing your website, I discovered that it is being served through Cloudflare.
See here: https://capture.dropbox.com/K6z41fMFZLoBdf7a
I recommend clearing/purging your site cache to ensure Cloudflare fetches a fresh version of files from your web server.
See here: https://developers.cloudflare.com/cache/
If the issue continues to occur,
Please temporarily disable your Cloudflare settings until you resolve your issue. And follow the next suggestion;
WooCommerce Permalinks
I found that you are using the WooCommerce plugin for your e-commerce platform.
Please check and reconfirm your Taxonomy Permalinks & Product Permalinks. Permalink settings for WooCommerce can be found at WordPress > Settings > Permalinks > Product Permalinks.
See here: https://woocommerce.com/document/permalinks/
Note: Please note that the product Custom base setting should NOT conflict with the Taxonomy permalink settings.
If all settings are set to the default option, and no issue has been found here, click the Save Changes button. Once you click the button, a confirmation text box will appear at the top of the page, telling you your settings have been saved.
See here: https://capture.dropbox.com/SnxEE8MVpwIQGLL4
I believe this will effectively solve your issue.
If the issue continues to occur,
Plugins Conflict
You may need to confirm if a plugin conflict causes the issue.
Deactivate all plugins except for WooCommerce → Try to Save the permalink again → Activate your rest of the plugins one by one (And confirm if any plugin is conflicting with your settings)
This must successfully resolve your issue.
If the issue continues to occur,
Review .htaccess File
You can review your .htaccess file. If you are unfamiliar with editing your .htaccess file, contact your hosting provider to ask them to turn on the mod_rewrite rules.
You can also refer to the htaccess documentation article by WordPress for further information.
See here: https://www.ads-software.com/documentation/article/htaccess/
If .htaccess is not writeable, your hosting provider will check your File Permissions and ensure that it can be read, write, modify, and accessed.
Reference
Below are a few WordPress references that will help you during the process.
Customize permalinks → https://www.ads-software.com/documentation/article/customize-permalinks/
Settings Permalinks Screen → https://www.ads-software.com/documentation/article/settings-permalinks-screen/
htaccess: https://www.ads-software.com/documentation/article/htaccess/
Changing File Permissions → https://www.ads-software.com/documentation/article/changing-file-permissions/
Let me know if your issue is still unresolved. I will be happy to assist you further in resolving your issue. Thanks. ??